Sh. Michaelson

Nanometer rough, sub-micrometer-thick and continuous diamond chemical vapor deposition film promoted by a synergetic ultrasonic effect

Abstract In this paper we report on a surface treatment to seed substrates for the promotion of diamond nucleation. This surface treatment consists of an ultrasonic abrasion process using poly-disperse slurry composed of a mixture of small diamond particles ( 3 μm) which may consist of diamond, alumina, titanium, etc. Whereas ultrasonic abrasion with a mono-disperse diamond slurry results in a diamond nucleation density of ∼2–3×108 particles/cm2, treatment with poly-disperse slurries results in diamond nucleation density of values up to ∼5×1010 particles/cm2. This effect was found to display a similar effectiveness on a variety of substrates such as silicon, sapphire, quartz, etc. The enhancement in diamond nucleation is interpreted by a ‘hammering’ effect whereby the larger particles insert very small diamond debris onto the treated surface, thus increasing the density of nuclei onto which diamond growth takes place during the chemical vapor deposition process. By increasing the nucleation density to values of ∼5×1010 particles/cm2, continuous diamond films of thickness of less than ∼100 nm were grown after only 5 min of deposition. The roughness of continuous diamond films grown on substrates treated at optimum conditions obtains values of 15–20 nm. The effect of ultrasonic treatment on silicon substrates and the deposited films was investigated by atomic force microscopy (AFM), high-resolution scanning electron microscopy (HR-SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy.

Hydrogen concentration and bonding configuration in polycrystalline diamond films: From micro-to nanometric grain size

The present work studies the incorporation of hydrogen and its bonding configuration in diamond films composed of diamond grains of varying size which were deposited by three different methods: hot filament (HF), microwave (MW), and direct current glow discharge (dc GD) chemical vapor deposition (CVD). The size of diamond grains which constitute the films varies in the following way: hundreds of nanometers in the case of HF CVD (“submicron size,” ∼300nm), tens of nanometers in the case of MW CVD (3–30nm), and a few nanometers in the case of dc GD CVD (“ultrananocrystalline diamond,” ∼5nm). Raman spectroscopy, secondary ion mass spectroscopy, and high resolution electron energy loss spectroscopy (HR-EELS) were applied to investigate the hydrogen trapping in the films. The hydrogen retention of the diamond films increases with decreasing grain size, indicating that most likely, hydrogen is bonded and trapped in grain boundaries as well as on the internal grain surfaces. Raman and HR-EELS analyses show that ...

Correlation between diamond grain size and hydrogen retention in diamond films studied by scanning electron microscopy and secondary ion mass spectroscopy

The present work studies the incorporation of hydrogen in chemical vapor deposited polycrystalline diamond films with different grain sizes. Scanning electron microscopy and secondary ion mass spectroscopy were applied to investigate the film microstructure and hydrogen retention in the films, respectively. The present study provides the direct evidence of hydrogen concentration dependence on diamond grain size. The hydrogen retention in the diamond films increases with decreasing grain size, indicating that hydrogen is bonded and trapped in the grain boundary region. The two different sources—methane and hydrogen molecules—contribute to the hydrogen retention according to their abundance in the gas mixture.

Determination of vibrational modes in electron energy loss spectroscopy of polycrystalline diamond surfaces by isotopic exchange

The high resolution electron energy loss spectrum of polycrystalline diamond films deposited from various isotopic gas mixtures, C12H4+H2, C12D4+D2, and C13H4+H2, are reported. Three types of peaks were unambiguously identified: (1) Pure C–C related peaks (a diamond C–C stretch at ∼150meV and its overtones at 300, 450, and 600meV), (2) pure C–H related peaks (C–H bend at ∼150meV and C–H stretch of sp3 carbon at 360meV), and (3) coupling of C–H and C–C peaks (∼510meV peak due to coupling of the C–H stretch at 360meV with either the C–C stretch or the C–H bend at ∼150–155meV).

Bulk and surface thermal stability of ultra nanocrystalline diamond films with 10-30 nm grain size prepared by chemical vapor deposition

The thermal stability of nanocrystalline diamond films with 10–30 nm grain size deposited by microwave enhanced chemical vapor deposition on silicon substrate was investigated as a function of annealing temperature up to 1200 °C. The thermal stability of the surface-upper atomic layers was studied with near edge x-ray absorption fine structure (NEXAFS) spectroscopy recorded in the partial electron yield mode. This technique indicated substantial thermally induced graphitization of the film within a close proximity to the surface. While in the bulk region of the film no graphitization was observed with either Raman spectroscopy or NEXAFS spectroscopy recorded in total electron yield mode, even after annealing to 1200 °C. Raman spectroscopy did detect the complete disappearance of transpolyacetylene (t-PA)-like ν1 and ν3 modes following annealing at 1000 °C. Secondary ion mass spectroscopy, applied to investigate this relative decrease in hydrogen atom concentration detected only a ∼ 30% decrease in the bulk content of hydrogen atoms. This enhanced stability of sp3 hybridized atoms within the bulk region with respect to graphitization is discussed in terms of carbon bond rearrangement due to the thermal decomposition of t-PA-like fragments.

Hydrogen incorporation processes in nanodiamond films studied by isotopic induced modifications of Raman spectra

The effect of replacing H by D and C-12 by C-13 in the gas species used to grow different types of nanodiamond films on the Raman spectra of these films was studied. The modifications of the Raman spectra were investigated in submicron sized diamond films grown by hot filament chemical vapor deposition and in nanodiamond films prepared by energetic glow discharge plasma. The latter are nanocomposites of nanodiamond crystallites embedded in an a-C:H matrix. The different spectra of the two film types add insight to the hydrogen incorporation processes in nanodiamond films responsible for the C–H related (assigned to trans-polyacetylene) Raman peaks.

Hydrogenation and thermal stability of nano- and microcrystalline diamond films studied by vibrational electron spectroscopy

The influence of high temperature annealing of hydrogenated diamond films with average grain size of ∼300 and ∼5 nm on surface degradation by graphitization is reported. Ex situ microwave plasma hydrogenation was applied to obtain fully hydrogenated diamond surfaces. Hydrogen bonding and near surface phase composition of both films were studied by high resolution electron energy loss spectroscopy (HR-EELS) and electronic EELS. C–H vibrational modes, phonon losses, and their overtones were measured by HR-EELS and bulk and surface plasmons by EELS. In situ vacuum annealing at 1000 °C results in hydrogen desorption and reconstruction of both kinds of surfaces, detected by vanishing of C–H peaks and appearance of sp2 hybridized carbon features. Our results suggest that graphitization induced by hydrogen desorption occurs to a larger extent on the surface of ∼5 nm grain size films. Subsequent in situ atomic hydrogen exposure of both films’ surfaces results in hydrogen adsorption and recovery of the diamond sur...

Enhanced electron field emission from preferentially oriented graphitic films

The electron field emission properties of nanographite films, whose basal planes display a degree of preferred orientation perpendicular to the surface, are reported. It was found that nanometric thick films which display a high degree of preferred orientation perpendicular to the substrate emit electrons at a high turn on field (TOF), while thicker films which display a much lower degree of preferred orientation emit electrons at a significantly lower TOF. It is suggested that the observed effect is mainly associated with the degree of basal planes orientation of the nanostructures and not just to their length.

Vibrational study of hydrogen bonding to ion irradiated diamond surfaces

High resolution electron energy loss spectroscopy has been used to probe hydrogenated diamond film surfaces exposed to 1keV Ar+ ions at a dose of ∼1015cm−2 and thermal annealing. The defects induced on the upper atomic layers were identified with regard to the different hydrogenated species hybridization states as well as their thermal stability. Ion irradiation resulted in the coexistence of a partially hydrogenated disordered near surface region including CH species bonded in sp, sp2, and sp3 bonding configurations and CC dimers. Thermal annealing of the ion beam irradiated hydrogenated surface leads to complete hydrogen desorption at ∼650°C. This temperature is significantly lower compared to a well defined diamond surface for which an annealing temperature above 900°C is needed.

Ion-induced electron emission from undoped sub-micron thick diamond films

The number of electrons emitted per impinging ion is known to be very high for hydrogenated B-doped diamond films. However, following ion bombardment the yield of emitted electrons rapidly decreases due to structural and chemical changes induced by the irradiation process. These changes eventually result in negative electron affinity loss and graphitization of the diamond film. Here we report results on ion-induced electron emission (IIEE) from undoped, sub-micron thick and hydrogenated diamond films. We found that the IIEE properties of these films are more stable upon similar bombardment conditions as compared to those of micron and sub-micron thick B-doped films. The enhanced IIEE properties of the sub-micron films are most likely associated with a reduced charging.